This massive metropolis in the center of China is at the heart of a virus outbreak that has gone global.

The first death from the new coronavirus outside of China.

The cruise ship, the Diamond Princess remains quarantined in Yokohama.

More than 71,000 people have been infected around the world.

In February, Chinese officials and state media touted a drop in the number of daily new confirmed cases.

(Speaking Chinese) The data of newly reported cases have been showing a downward trend.

But only hours later, local authorities released data showing a dramatic jump, partially due to a shift in the way new cases were diagnosed and confirmed.

While the authorities said the goal behind the new criteria was to let more patients receive better treatment, this raised concerns that the scale of the outbreak has been larger than Chinese data had earlier suggested.

We thought there was better transparency coming out of China but it doesn't appear to be.

In response to the criticism, Beijing said it has been active and open toward cooperation with international experts.

To independently assess the scale of the disease, groups of scientists around the world have been using mathematical modeling and their estimates so far exceed the officially reported numbers.

The new virus was first detected in December, and by mid-January, the number of cases was just over 40, but epidemiologists across the world thought that something wasn't right when three cases were confirmed outside of China.

How could we have three or seven exported cases when there seemed to be relatively small numbers?

Christl Donnelly and her colleagues at the Imperial College London looked at the number of cases outside China, which they call exported, to calculate the scale of the outbreak.

Wuhan's a big city.

It has 19 million people in the metropolitan area and it has an international airport and it's interconnected.

So there're flights and people traveling to lots of places.

They used similar mathematical modeling developed during the H1N1 influenza outbreak in Mexico in 2009.

If you look at the number of cases that have been exported and then there is a factor which you can use to then estimate the number of cases that there were in the source region.

Before the virus shut down the city, the international airport operated flights to dozens of major cities worldwide with more than 3,000 passengers traveling through the airport every day.

The researchers also assumed that 10 days likely passed between a person getting infected and the disease being detected.

But you can get an idea by looking at the number of flights that came out, you know, what's the population size?

How many departures, international departures do you have on a given day?

The Imperial College researchers estimated that over 1,700 people could have been infected in Wuhan by mid-January, indicating a massive gap between China's 41 confirmed cases reported at that time and their estimates.

Other researchers did similar calculations based on the exported overseas cases and with several other variables and came to similar results.

In later reports, scientists factored in new data and their numbers were still much bigger than Beijing's official tally of confirmed cases.

These findings give a rough picture and the margin of error remains high in part because of other factors like the fact that human-to-human transmission was confirmed overseas.

Many people in China have been critical of how Beijing has dealt with the crisis and have been skeptical about the official data.

Donnelly says that the Imperial College's analysis is not aimed at criticizing Beijing's efforts but trying to look at what was going on and what might be expected from the virus.

She says that there are a myriad of reasons why China's figures might not reflect reality.

It's difficult for any country, if a new disease starts in your country, there's a lot to be identified to begin with so when you first start, you really don't know what the potential is.

What makes it even harder to diagnose the coronavirus is that people infected may show very mild symptoms like fever and coughing that are also common in other types of infections.

In an effort to battle the virus, Beijing has spent about 800 million USD, deployed thousands of medical staff and built two field hospitals in days.

China is doing many good things that's slowing the virus and this has to be recognized.

While the WHO repeatedly praised China, other public health experts have been more critical.

It took the agency nearly two weeks to get a go-ahead from Beijing to send a group of experts to China to conduct joint research with Chinese scientists.

Epidemiologists say they're still learning about the new virus and hope their research will help officials in China to put effective measures in place to tackle the outbreak.

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